The invention relates to formation of a recess adjacent to a blade tip of blades mounted in turbines, compressor rotors, or fan blades, in a gas turbine engine.
In order to tune the blades to achieve dynamic benefits such as vibration stress reduction and weight reduction, the prior art has included recesses in the air foil surfaces of blades. The high rotary speeds and dynamic interaction with gas flow creates simultaneous need for weight reduction, maintenance of aerodynamic performance, measurement of blade creep growth but primarily for balancing dynamic vibratory effects.
For example, U.S. Pat. No. 4,265,023 provides a creep growth notch machined or cast adjacent to the tip of the air foil for measuring creep growth of the blade under stress. In order to increase the vibration mode frequency, prior art blades have included removal of material from the air foil extending to the blade tip.
A disadvantage of the prior art method is that the geometry of the tip of the blade is an important factor in determining the aerodynamic properties of the blade, the structural integrity of the blade and the maintenance of appropriate clearances with a surrounding shroud.
It is an object of the present invention to provide a means for increasing the natural frequency of the blade while maintaining the structural integrity, aerodynamic properties and castability of the blade.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.